Originally Posted by BMWTurboDzl
Heat and the fact that there still is some air in the unit. The article doesn't say that the units can run forever with out an ATF change.
The article does seem to separate water/dirt from air. Breathers allowed some air but kept water/dirt out. Engineering of the breathers to reduce the amount of air to only what's required is an advancement in itself. I any case the trick to reading Wiki is to hit the citations in order to obtain a deeper understanding.
The article makes sense to me because I remember years ago where the ATF dipstick on my late model vehicles were always just kind of loose fitting.
You have to understand that the transmission will have as much air as there is free space not occupied by other things like ATF, gears etc. and it is at equilibrium with the atmospheric pressure. Not just "some" air. Some air would be referred to when a system is filled with "some" air and then hermetically sealed. That is not the case with transmissions. The breather does not limit air movement, the air movement is dictated by the inside workings of the transmission. Spinning gears will create air drafts, expanding ATF will displace air above etc. Even the initial start up will create a big air movement as the ATF is being pumped though some of the empty passages that drained during shut off period.
The breather ensures that the air is free to move in or out without ingesting water and other contaminants. It does not limit air movement, because if it did, the air would find some other way to enter/escape, but that would not be controlled, so other contaminants would likley be carried over as well, plus depending on the location, a loss of ATF.
Heat and the fact that there still is some air in the unit. The article doesn't say that the units can run forever with out an ATF change.
The article does seem to separate water/dirt from air. Breathers allowed some air but kept water/dirt out. Engineering of the breathers to reduce the amount of air to only what's required is an advancement in itself. I any case the trick to reading Wiki is to hit the citations in order to obtain a deeper understanding.
The article makes sense to me because I remember years ago where the ATF dipstick on my late model vehicles were always just kind of loose fitting.
You have to understand that the transmission will have as much air as there is free space not occupied by other things like ATF, gears etc. and it is at equilibrium with the atmospheric pressure. Not just "some" air. Some air would be referred to when a system is filled with "some" air and then hermetically sealed. That is not the case with transmissions. The breather does not limit air movement, the air movement is dictated by the inside workings of the transmission. Spinning gears will create air drafts, expanding ATF will displace air above etc. Even the initial start up will create a big air movement as the ATF is being pumped though some of the empty passages that drained during shut off period.
The breather ensures that the air is free to move in or out without ingesting water and other contaminants. It does not limit air movement, because if it did, the air would find some other way to enter/escape, but that would not be controlled, so other contaminants would likley be carried over as well, plus depending on the location, a loss of ATF.